Field of the Invention
The present invention relates to a light source unit which is able to emit light which is less influenced by interference fringes and which is suitable for a projector.
Description of the Related Art
In these days, data projectors are used on many occasions as an image projection apparatus which projects images including an image of a screen and a video image of a personal computer, as well as images based on image data which is stored on a memory card on to a screen. In these data projectors, light emitted from a light source is caused to converge to a micromirror display element called a DMD (Digital Micromirror Device) or a liquid crystal panel so that a color image is displayed on a screen.
Conventionally, the mainstream of these projectors has been those which utilize a high-intensity discharge lamp as a light source. In recent years, however, there have been made many developments on using red, green and blue light emitting diodes or laser diodes, or solid light emitting elements using organic electroluminescence as light sources, and many proposals have been made.
Then, a light source unit which employs laser diodes can easily be made small in size and can constitute a small and high-intensity light source unit. However, in a projection image formed by laser beams, interference fringes are generated, and the interference fringes so generated deteriorate the quality of the projection image from time to time.
To cope with this problem, for example, the Japanese Unexamined Patent Publication (KOKAI) No. 2008-185628 (JP-2008-185628 A) proposes a light source unit including a combination of a dividing device which divides a wavefront which is emitted from a light source, a converting devise which rotates the plane of polarization of a bundle of light rays at the divided wavefront, and a combining device which superposes the wavefronts of the bundles of light rays of which the planes of polarization are oriented differently.
However, in this light source unit, the light emitted from the light source is once divided, and the planes of polarization of the light so divided are rotated and are thereafter superposed to be shone on to a predetermined plane, and therefore, the light source unit becomes complex and the production thereof is not easy.